The present invention relates to a driving apparatus for a rolling mill called a pair cross mill, and more particularly relates to an improved driving apparatus which is for a rolling mill called a pair cross mill and in which work rolls are coupled to driving shafts through universal joints.
FIG. 3(a) is a simplified plan view of a conventional driving apparatus for a rolling mill called a pair cross mill.
FIG. 3(b) is a simplified front view of the driving apparatus.
The rolling mill includes upper and lower work rolls 1 and 2 which appear to extend across each other when viewed vertically from the top but appear to extend parallel to each other when viewed horizontally from the front. That is, the axes of upper and lower work rolls 1 and 2 lie in planes parallel to the plane of a workpiece between upper and lower work rolls 1 and 2, and are slanted in opposite directions with respect to the longitudinal axis of the workpiece.
The driving apparatus includes a motor not shown in the drawings, upper and lower driving shafts 3 and 4, upper and lower intermediate shafts 5 and 6, two upper universal joints 7A and 7B, and two lower universal joints 8A and 8B. The driving shafts 3 and 4, which are driven by the single motor, appear identical when viewed vertically from the top, but appear to extend parallel to each other when viewed horizontally from the front. The upper and the lower work rolls 1 and 2 are coupled to the upper and the lower driving shafts 3 and 4 by the upper and the lower intermediate shafts 5 and 6 and the upper and the lower universal joints 7A, 7B, 8A and 8B, respectively. The upper driving unit of the driving apparatus includes the upper driving shaft 3, the upper intermediate shaft 5 and the upper universal joints 7A and 7B. The lower driving unit of the driving apparatus includes the lower driving shaft 4, the lower intermediate shaft 6 and the lower universal joints 8A and 8B. The upper and the lower driving units are disposed symmetrically with regard to horizontal and vertical planes Z.sub.1 and Z.sub.2. Since such universal joints are relatively low in cost of acquisition and maintenance and high in motive power transmitting property, studies are being made to use the joints for the pair cross rolling mill as well as for ordinary rolling mills.
To equalize the rotation speeds of the driving shafts 3 and 4 and the work rolls 1 and 2 to each other, the following conditions must be met: (1) the yokes of the upper universal joints 7A and 7B are attached at identical angles to the end of the upper intermediate shaft 5, and the yokes of the lower universal joints 8A and 8B are attached at identical angles to the other ends of the lower intermediate shaft 6; (2) the shaft operating angle of the universal joints 7A and 7B to be paired are equal and the shaft operating angle of the universal joints 8A and 8B to be paired are equal; and (3) the axes of the components of the upper driving unit are coplanar, and the axes of the components of the lower driving unit are coplanar. However, since for the pair cross mill more importance is attached to the single motor being used as a driving power source for the two driving shafts 3 and 4, the installation space for the driving apparatus is minimized by reducing the width l of the apparatus. For that reason, the above-mentioned conditions need to be partially ignored in some cases. In those cases, the phase angles of the work rolls lead and lag each other. In reality, however, the phase angles of the work rolls 1 and 2 not only lead and lag each other, but also they are 90 degrees out of phase with each other, as shown in FIGS. 4(a) and 4(b), due to the fact that the direction of rotation of the upper work roll 1 and the direction of rotation of the lower work roll 2 are opposite to each other. For that reason, the slip of a workpiece between the upper and the lower work rolls 1 and 2 becomes so large that the driving apparatus cannot be put in practical use even in the case of rolling at the low speed, the case of rolling of the thick plate, or the like. This is a problem.